Devices for measuring the dimensional changes of an object due to the mechanical or thermal stress or a combination of both are typically referred to as strain gauges or strain sensors. Strain sensors have various types such as: optical fiber strain sensors, piezoelectric ceramic strain sensors and electromechanical strain sensors. The electromechanical strain sensors are fabricated by conductive polymers or polymer composites with conductive fillings.
US application 20060148351 (Tao; Xiaoming; et al. J; and De Rossi et al. in “Materials Science Engineering, C”, 7(1), 31-35 (1998), “Dressware: Wearable Hardware” and “IEEE Sensors Journal 2003”, 460-467, “Strain-sensing fabrics for wearable kinaesthetic-like systems”, introduced strain sensors made of conductive polymer coated fabric. However, due to the conductive polymer used, the environmental and chemical stability of the sensor is a problem in long term applications.
De Rossi et al. in “Autex Research Journal 2002”, 2(4):193-203, “Smart textiles for wearable motion capture system”, and in “IEEE Sensors Journal 2004”, 807-818, “Wearable, redundant fabric-based sensor arrays for reconstruction of body segment posture”, reported strain sensors to measure body segments made of carbon loaded silicon rubber coated fabrics. However, the sensors exhibited a low gauge factor of 2.5. The higher gauge factor is proffered for strain sensors. The fatigue test of the strain sensors was not addressed in these reports.
In “MateriaLs Science Forum 2007”, 537-538 and 709-716; and “High elastic strain gauge made from conductive silicon rubber”, Laszlo et al, introduced methods to fabricate large strain gauge from conductive silicon rubber. The structure of the 35 sensor is a pure polymer and not fabric and the sensor exhibits Low sensitivity.
In U.S. Pat. No. 4,567,093 (Sogabe, et al.), US application 20050282453 (Jackson, Scott Richard, et al.) and US application 20060286390 (Yaginuma; Atsushi, et al.), methods and applications of the coated fabrics as airbags and protected fabrics are disclosed. But no sensors are disclosed in the US patent or applications.
In U.S. Pat. No. 6,660,978 (Avdeev, U.S. Pat. No. 4,705,646 (DuPont et al. and U.S. Pat. No. 5,009,927 (Cloyd et al.), conductive particles were added into the coated polymer to render the fabric electrical conductivity properties. These properties have suggested it is used in the control of static charges, heating, electrical conducting, and electromagnetic wave shielding. However, no sensors are disclosed in these US patents.
Using electrically conductive elastomer composites coated on elastic fabric as strain/pressure sensors can be limited. Examples of limitations of using electrically conductive elastomer composites for sensors that can be encountered, which are not coated on fabric, include sensors which exhibit low sensitivity and linearity. In addition, electrically conductive elastomer composites coated on fabric are typically not used in sensor applications. Therefore electrically conductive elastomer composites suitable for use as flexible strain/pressure fabric sensors and a method for manufacturing the same is highly desirable.